I believe you have a point. It is far more easier to deal with rejection via a website than face to face. By the same token dating sites also gives both genders the opportunity to approach each other in higher numbers. A woman is more likely to approach a man using her screen name online then she would in public.
Another fact about dating sites is people put their profiles up there because they are "looking" to meet others! It takes the guess work out of it compared to meeting someone out in public. You don't know if they are married, in love with someone, or taking a break from relationships. Not knowing increases your odds of being rejected. At some point as we get older standing in line to get into some over crowded nightclub, sitting around in a piano bar lounge looking at the door way, counting on family and friends to introduce you to someone, or joining various hobby clubs and taking classes with the hope of one day meeting "the one" gets old, time consuming, and expensive. People would rather stay home scan profiles and reach out to multiple people that interest them and see what becomes of it.